Trailing in the polls and struggling on the campaign trail, Mitt Romney got a much-needed jolt of energy Wednesday with a strong performance in the first debate with President Obama.

Appearing on stage alongside the incumbent Democrat for the first time, the Republican nominee appeared relaxed, in command of facts and persistently on the offensive during the 90-minute encounter at the University of Denver. Obama, who has not debated in four years, looked rusty and found himself responding to the policy agenda set by Romney.

“Given what was at stake, Mitt Romney had a very good debate,” said David Lanoue, a political scientist at
Columbus State University in Georgia. “He was sympathetic, he was focused, and he attacked the president’s record without being disagreeable. If debates really do have an impact, this one should certainly help Romney.”

The former Massachusetts governor took the offensive from the beginning, accusing Obama of engaging in “trickle-down government,” a play on the Democratic attack on Republican “trickle-down economics.” Romney, who has been accused of failing to discuss policy specifics, listed specific priorities, even if he remained fuzzy about programmatic details.

“Romney was on offense most of the night, holding Obama accountable for massive investments in green energy, the growing national debt and weak economic recovery,” said Republican consultant Matt Mackowiak. “President Obama appeared confused, off his game, unsure and unprepared, failing to make one memorable statement. Obama never asked Romney to defend the Bain record, his decision to release only two years of tax returns or the ’47 percent’ comment.”

Bill Galston, a former policy adviser to Bill Clinton, said Romney “did himself considerable good” in Denver.

“Romney presented himself as a reasonable man—neither an extremist nor an ideologue,” said Galston, a senior fellow at the Brookings Institution. “He calmly rebutted familiar attacks on his proposals. He was clear and forceful, tough but respectful. He sounded knowledgeable. He conveyed an impression of competence and experience as a potential manager of the economy. He praised some aspects of the Obama administration’s program, such as its Race to the Top education reform program. And when he insisted on the importance of working together across party lines, it sounded as though he meant it.”

Another former Clinton adviser, James Carville, said the debate had breathed new life into Romney’s troubled campaign.

“What happened tonight will play out clearly throughout the weekend and into the next debate,” he said Wednesday night.

Other prominent Democrats downplayed the debate, pointing to the lack of a major gaffe on the incumbent’s part.

“Romney needed a game changer,” San Antonio mayor Julian Castro, the Democratic National Convention keynote speaker, declared via Twitter. “Obama easily won, since Romney didn’t land any blows. Nothing changed the dynamic of the race.”

But nonpartisan commentators seemed to agree with former George W. Bush adviser Karl Rove, who tweeted, “One guy was presidential, focused, passionate and funny. The other guy was churlish, irritated and defensive.”

One veteran debate analyst said the Republican challenger prevailed both on debate points and policy substance.

“I believe Gov. Romney won the debate because he was the aggressor and on offense for most of the debate,” said Aaron Kall, director of debate at the University of Michigan. “President Obama is not used to being challenged by others and his nearly four year absence from presidential debating was very evident. President Obama engaged in a four corners basketball strategy and tried to run out the debate clock. Gov. Romney probably wished the debate had gone on for another ninety minutes.”

Also contributing to this report were Summer Ballentine and Kyle Campbell of the Hearst Newspapers Washington bureau.